A typical example of a rotor-stator device is provided by a computer tomograph (CT). A computer tomograph normally comprises a slewing ring which can be rotated relative to a stationary suspension and to which an X-ray source (X-ray tube) and a radially opposite (X-ray) detector are connected. The slewing ring rotates as instructed about an object that is to undergo X-ray examination, and the X-radiation which is emitted and modified during the X-ray examination of the object is detected by the detector. The combination of a rotating slewing ring and a stationary suspension of the slewing ring is referred to collectively as a “gantry” in the following.
A so-called slip ring arrangement is normally used to transfer measurement and control data between the rotating part and the stationary part of the gantry. The slip ring arrangement typically comprises a ring-shaped transfer element (referred to in the following as a signal conductor), which is fastened to the rotating part or to the stationary part of the gantry. The signal conductor is often segmented over its circumference, such that each signal conductor segment can provide a separate data channel. The slip ring arrangement further comprises a number of transmitters and receivers, which are used to inject data into and read data out from the signal conductor or the respective signal conductor segment.
A direct sliding contact (mechanical) or a method based on capacitive coupling is generally used as a means of transfer between transmitter/receiver and signal conductor. Optical transfer methods are likewise known.
In addition, the gantry is usually assigned an angle measuring system which is used to determine the current angular position of the rotating part of the gantry in each case. The knowledge of the current rotational position of the slewing ring is firstly required for the purpose of activating a motor which drives the slewing ring, particularly if an electronically commutated direct drive is used. The knowledge of the current angular position is also required in order to ensure the correct recording (in the case of a position-triggered system) or the correct interpretation of the recorded measurement data (in the case of a time-triggered system).
The angle measurement is usually performed using a measurement standard which is applied to the circumference of the rotating part of the gantry and is optically or inductively interpreted by a measuring head.
DE 10 2004 042 486 A1 discloses a device for measuring the angle of rotation of a rotor in relation to a stator, wherein a disk which is provided with markings can be rotated relative to a detection entity for the purpose of detecting the markings.